Electrical slip ring having a higher circuit density

ABSTRACT

Disclosed is a method of manufacturing a slip ring printed circuit board which includes forming a plurality of concentric spaced electrical contacts on one side of a non-conductive base and forming interconnecting electrical paths on an opposite side of the non-conductive base. The method of manufacturing a slip ring printed circuit board also includes electrically connecting the electrical contacts and the interconnecting electrical paths, depositing copper on the electrical contacts to form electrical rings and etching a groove into each of the electrical rings.

FIELD OF THE INVENTION

The present invention relates generally to electrical slip rings, andmore particularly, to an electrical slip ring having a higher circuitdensity than prior art. Advantageously, the present invention isdirected to flat composite electrical slip ring in which the electricalrings are spaced in close proximity to each other.

BACKGROUND OF THE INVENTION

Electrical slip rings are well known devices for communicatingelectrical signals from one structural member to another where one ofthe structural members is rotatable with respect to the other. Such aslip ring apparatus, for example, may comprise a relatively stationaryannular base member, which has a plurality of conductive rings extendingannularly there around. One or more electrically conductive brushes arearranged on a relatively rotatable structural member to rotate about thestationary annular base member and each of the brushes is arranged tocontact a surface of one of the conductive rings thereby forming aseries of electrical connections between the two structural members.

A flat or “pancake” slip ring is such a device of minimal height orthickness for military or commercial environments where space for theslip ring is very limited. The conductive rings forming the slip ringbase generally are formed from materials having a thickness from 0.003to 0.040 inches with most such materials having a thickness in the rangeof 0.006 to 0.016 inches. Characteristically, the rings for such a slipring base are approximately 0.015 to 0.020 inches in width. Spacesbetween the rings or the ring pitch are characteristically approximatelyof the same dimension.

A grooved plate process is the most common method of manufacturingpancake slip rings. In the grooved plate process, a grooved plate isprepared by rough machining a brass plate to approximately a “groovedplate” shape. The grooved plate is then annealed to minimize distortionduring subsequent plastic curing and final machining. One side of thegrooved plate is then machined to final “grooved plate” shape. Peakscorrespond to the bottom of the future rings, and valleys correspond tothe future insulation barriers between rings. The “grooved plate” isthen plated with nickel and a gold strike. A lead wire is soldered orwelded to individual ring features on the grooved plate. A glass clothis then bonded to the plate to prevent leads from entering the valleysof the plate (the future barriers between rings). The plate and leadassembly is then loaded into a metal mold which contains features toprovide for internal lead routing, lead exist positioning, and otherrotor geometry requirements. The mold is vacuum cast with a liquid epoxyto completely fill the internal detail of the mold. At this point, theassembly is a single piece with a continuous plate on one or two sideswith internal epoxy insulation. The final machining step turns theexposed surface of the plate to separate the plate into individualconcentric rings separated from each other with epoxy (filling theformer valleys in the plate). After the rings are separated, insulatingbarriers between the rings are machined to final dimensions. Inaddition, at this step the ring surface is machined to final dimension.The ring groove pattern may be V, U or double-V shaped. In addition toring shape, the rings are machined to the required surface roughness.The rotor is then nickel plated and then plated with precious metal(usually gold or silver). This process is complex and the density ofslip rings is limited by the machining requirements.

An electroformed rings process is another known process. A rotor andlead assembly is prepared by loading lead wire into a mold whichcontains features to provide for internal lead routing, lead exitpositioning, and other rotor geometry requirements. The mold is castwith a liquid epoxy to completely fill the internal detail of the moldand encapsulate the lead wires. Grooves are machined which will containthe rings. Starter rings are prepared as follows. At the bottom of thering groove, the lead wire conductor is exposed and prepared (generallyby applying a fillet of conductive epoxy). The inside walls of the ringgroove are coated with conductive plastic to form a continuousconductive starter ring for plating. The ring is electroformed byplating copper onto the starter ring using high build platingtechnology. High build plating technology or high buildup electroformingis a method of creating a thicker ring cross-section by plating up thestarter ring, usually in a copper bath. The starter rings may be platedup with or without dielectric barriers between the rings. At this point,the assembly is a single piece with discrete rings and leads embedded inepoxy insulation. The final machining step will form final shape andtexture of the rings and insulating barriers between the rings. Thefinal rotor is nickel plated and then plated with precious metal(usually gold or silver). The disadvantages of the electroformed ringsprocess include limited ring thickness buildup unless barriers arepresent. Extensive machining is required to create dielectric barrierswhich allow a buildup of thicker rings. Due to the lengthy timesrequired to electroform the rings, plating solution can damage the slipring materials, leak into loads embedded in the dielectric causing leaddamage and electrical insulation failures. Dielectric materials caninterfere with the electroforming process. Ring sides cannot be sealedwith nickel allowing corrosion products to form and contaminate theelectrical contacts. The contaminants will lead to contact failure andelectrical shorts. This is the most significant drawbacks ofconventional electroformed rings.

More recent requirements using an electrical slip ring assembly in aForward Looking Infrared Radar (FLIR) platform have severe spacerequirements than can be accommodated by either of the grooved plateprocess or the electroformed rings process. The FLIR systems are usedfor surveillance, reconnaissance, rangefinder, targeting, and firecontrol applications. These FLIR platforms all impose severerequirements on the electrical slip ring, including a high circuitdensity in which many circuits are required and space for the slip ringis always limited. Another requirement is for high bandwidth and lownoise for the digitized video signals that pass through the electricalslip ring assembly. Yet another requirement is for low temperatureoperations in which the electrical slip ring assembly can function overthe temperature range of −54° C. to +60° C.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a flat compositeelectrical slip ring having a higher circuit density than prior art sliprings.

It is another object of the present invention to provide an electricalslip ring apparatus in which the electrical slip rings are notmechanically machined.

It is yet a further object of the present invention to provide anelectrical slip ring which is reliable on the operation, easy tomanufacture and cost effective.

These and other objects of the present invention are achieved usingthree related processes. These processes include double-sided printedcircuit board technology, copper electroforming, and chemical machining.Using the present invention, double-sided copper clad glass reinforcedepoxy laminate (FR4) is coated with a photosensitive polymer that isimaged using a photographic negative. Following exposure with an intenseultraviolet light source, the photosensitive polymer is then developedwith solvent that selectively dissolves away unexposed areas of theresist. When the resist is removed, copper is exposed for subsequentetching.

The photo imaged material is then placed in a copper etchant thatremoves the exposed copper. Areas protected by the photoresist areunetched and form the interconnecting electrical passages on one side.Holes are subsequently drilled through the etched material toelectrically connect the two sides. The connections are formed utilizingplated through-hole processes and/or by filling the holes with aconductive material, such as silver filled epoxy.

Once the through-hole interconnections are formed, photoresist is againapplied to both sides of the slip ring circuit boards. A single layer ofresist is applied to the electrical interconnects and multiple layersare sequentially applied to the opposite side. The multiple layers ofphotoresist are then exposed with ultraviolet light through a photo toolcontaining multiple concentric rings. After the image is developed,copper is then electroformed up between the concentric rings ofphotoresist to form the copper rings. After the resist between theelectroformed rings is removed, the electroformed rings are subsequentlyseparated by etching away the thin layer of copper between the base ofthe rings. Electro formed rings are subsequently recoated withphotosensitive polymer and reimaged with a photo tool to allow etchingof U-grooves in the ring. These grooves, after a gold allow plating,including small percentage of nickel is applied, form the contactsurfaces for the mating brush contacts. The nickel in the allow platingsignificantly increases the hardness and wear resistance of the goldelectrodeposit while maintaining a low electrical contact resistance.The nickel also promotes chemisorption of the lubricant, thus furtherreducing contact wear.

The slip ring is then mated with brush blocks to form a slip ringapparatus. The resulting slip ring apparatus has a higher circuitdensity than is readily achievable with conventional slip ringmanufacturing methods while having a lower per circuit cost.

The foregoing objects of the present invention are also achieved bymanufacturing a slip ring printed circuit board including forming aplurality of concentric spaced electrical contacts on one side of anon-conductive base and forming interconnecting electrical paths on anopposite side of the non-conductive base. Manufacturing a slip ringprinted circuit board also includes electrically connecting theelectrical contacts and the interconnecting electrical paths, depositingcopper on the electric contacts to form electrical rings and etching agroove into each of the electrical rings.

The foregoing objects of the present invention are also achieved by amethod of manufacturing a slip ring printed circuit board includesforming a plurality of concentric spaced electrical contacts on one sideof a non-conductive base and forming interconnecting electrical paths onan opposite side of the non-conductive base. A method of manufacturing aslip ring printed circuit board also includes electrically connectingthe electrical contacts and the interconnecting electrical paths,depositing copper on the electrical contacts to form electrical ringsand etching a groove into each of the electrical rings.

The foregoing objects of the present invention are also achieved by anelectrical slip ring apparatus includes an annular base member and atleast one brush block assembly secured to the annular base member havinga plurality of brushes. A flat composite electrical slip ring includesan electrically non-conductive base and a plurality of concentric spacedelectrical rings located on one side of each of the electricallynon-conductive base. The slip rings are spaced from adjacent electricalrings at a distance of approximately 0.70 or greater. Interconnectingelectrical paths are located in an opposite side of the electricallynon-conductive base. Connecting means are provided for connecting atleast some of the electrical rings to the interconnecting electricalpaths.

The foregoing objects of the present invention are also achieved by aflat composite electrical slip ring product produced by the methodincludes forming a plurality of concentric spaced electrical contacts onone side of a non-conductive base and forming interconnecting electricalpaths on an opposite side of the nonconductive base. The foregoingobjects of the present invention are also achieved by a method ofmanufacturing a slip ring printed circuit board also includeselectrically connecting the electrical contacts and the interconnectingelectrical paths, depositing copper on the electrical contacts to formelectrical rings and etching a groove into each of the electrical rings.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in the art from the following thedetailed description, wherein the preferred embodiments of the inventionare shown and described, simply by way of illustration of the best modecontemplated of carrying out the invention. As will be realized, theinvention is capable of other and different embodiments, and its severaldetails are capable of modifications in various obvious respects, allwithout departing from the invention. Accordingly, the drawings are tobe regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not bylimitation, in the figures of the accompanying drawings, whereinelements having the same reference numeral designations represent likeelements throughout and wherein:

FIG. 1 is a side cross-sectional elevational view of an electrical slipring device;

FIGS. 2A and 2B are top plan and bottom plan views of an electrical slipring apparatus according to the present invention;

FIG. 3A is a side elevational view of a composite electrical slip ring;

FIG. 3B is an enlarged side cross-sectional elevational view of thecomposite electrical slip ring apparatus according to the presentinvention;

FIG. 4A depicts a brush block assembly according to the presentinvention;

FIG. 4B is a side elevational view of a brush of FIG. 4A taken alongline 4B—4B in FIG. 4A; and

FIGS. 5A-5L depict the steps of manufacturing an electrical slip ringaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, an electrical slip ring apparatus 10 isdepicted. The electrical slip ring apparatus 10 is depicted in FIG. 1with the electrical slip rings extending vertically, although it shouldbe understood that the present invention is usable in any orientation.Accordingly, terms such as “above”, “below”, “right”, and “left”, asused herein, are to be construed in the relative sense. The presentpatent application incorporates by reference in its entirety into thisspecification, U.S. patent application Ser. No. 08/887,697 filed Jul. 3,1997, entitled “METHOD OF MANUFACTURING A FLAT SLIP RING ASSEMBLY”, andassigned to the instant assignee.

The electrical slip ring apparatus 10 includes a cylindrical housing 20including three stacked electrical slip ring assemblies 30, 32, 34according to the principles of the present invention. Although threeslip ring assemblies are depicted any number of slip ring assemblies canbe used. The slip ring assemblies 30, 32, 34 can be identical but neednot be identical depending on the application. Each electrical slip ringassembly 30, 32, 34 has an annular body 36, 37, 38 secured to thehousing 20 and an electrical slip ring 41, 42, 43, respectively. Asdepicted in FIG. 1, the cross-section of the bodies 36, 37, 38 areU-shaped. The electrical slip rings 41, 42, 43 are freely rotatablerelative to the bodies 36, 37, 38 and each is connected to a rotatablehub 48 for rotation therewith. A plurality of shields 44, 45, 46 arelocated inside the housing 20 and are connected to the housing 20. Theshields 44, 45 are positioned between electrical slip ring assemblies30, 32 and 32, 34, respectively. For example, body 38 is formed in twohalves 49, 50. Each half 49, 50 has a radially inwardly extending flange51, 52, respectively, forming a cylindrical opening 53. A plurality ofbolts are used to connect the slip ring assemblies 30, 32, 34 andshields 44, 45, 46. The electrical slip ring apparatus 10 is otherwiseconventional and is not described in detail herein.

Refer now to FIGS. 2A and 2B which depict opposite sides of any one ofthe electrical slip ring assemblies 30, 32, 34 but for brevity onlyelectrical slip ring assembly 30 is described. The electrical slip ringassembly 30 includes the electrical slip ring 41 which includes twopreferably identical electrical slip ring halves 54, 56 bonded togetherand two preferably identical brush block assemblies 62, 64. The brushblock assemblies 62, 64 are fixedly connected to the flanges 51, 52,respectively and extend radially inwardly therefrom. The electrical slipring halves 54, 56 can be of different configurations. The brush blockassemblies can also be of different configurations. The brush blockassemblies 62, 64 are pie shaped with one edge fixedly connected to acorresponding flange 51, 52. Each brush block assembly 62, 64 iscantilevered from the flange 51, 52 and so rigidity of the printedcircuit board of each brush block assembly 62, 64 is important in orderto maintain uniform contact between the brushes and their respectiveelectrical slip rings. The annular body 36 and brush block assemblies62, 64 remain stationary relative to the housing 20 during the operationof the electrical slip ring apparatus 10 while the electrical slip ringassemblies 30, 32, 34 rotate. The brush block assemblies 62, 64 arelocated on opposite sides of the composite electrical slip ring 50 andare angularly spaced from each other in a circumferential direction. Aplurality of leads 82 are electrically connected at an inner peripheryof the electrical slip ring 41 to a rotary member (not shown). Eachelectrical slip ring half 54, 56 has a plurality of concentric radiallyspaced electrical rings 84. Each brush block 62, 64 has a plurality ofbrushes 80 and is electrically connected to a corresponding plurality ofleads 90. The leads 90 are soldered to corresponding connecting points150. The electrical slip ring 50 has diametrically opposite radial slots72, 74 for engaging the hub 48.

Refer now to FIG. 3A where a composite electrical slip ring 50 isdepicted, according to the present invention, connected to the hub 48.As depicted in FIG. 3B, the composite electrical slip ring 50 includesthe two electrical slip ring halves 54, 56 bonded together with epoxypolyamide adhesive to form the composite electrical slip ring 41. Asdepicted in FIG. 3B, the slip ring halves 54, 56 have a plurality ofconcentric spaced electrical rings 84. Each ring 84 has a groove 86 forreceiving a corresponding brush 80. The groove is defined by a pair ofside walls 89 and a radiused surface 91 connecting the sidewalls 89.Each of the electrical slip ring halves 54, 56 has a back surface 93, 94to which electrical interconnecting circuits 95, 96 are located.

Refer now to FIGS. 4A and 4B which depict one of the brush blockassemblies 62. The brush block assembly 62 is mounted on a printedcircuit board 100. Because of the high circuit density of the electricalslip ring, the brush block 62 must also be formed with a high circuitdensity corresponding to the circuit density of the electrical slip ring41. To accommodate the high circuit density, the printed circuit boardis preferably formed of multiple layers (three layers 122, 132, 142 aredepicted in FIG. 4B, although any number of layers can be used) ofcircuit boards each having circuit traces formed thereon.Advantageously, the use of multiple layers between each layer of circuitlayers provides a ground plane between each layer of circuit layers. Asdepicted in FIG. 4A, there are three sets of circuit traces, eachconnected to a corresponding brush 80. A first set of circuit traces 120(indicated by solid lines) is on a first layer 122, a second set ofcircuit traces 130 (indicated by long dashed lines) is on a second layer124, and a third set of circuit traces 140 (indicated by short dashedlines) on a third layer 142 carries an electrical signal to/fromconnection points 150 on the printed circuit board 100 of the electricalslip ring apparatus 10 to/from a corresponding brush 80. The printedcircuit boards are preferably formed of glass reinforced epoxy laminate(FR4) and are bonded together using an epoxy polyamide cement.

As depicted in FIG. 4A, printed circuit board 100 has a pie shapedconfiguration having a circumferentially extending portion 155 and tworadially inwardly extending portions 160, 162. Connection points 150 arelocated on the circumferentially extending portion 155 and the brushblocks 80 are mounted to each of the radially inwardly extendingportions 160, 162 and extend circumferentially outwardly beyond theprinted circuit board 100. The leads 90 are soldered to connectionpoints 150.

Each of the brushes 80 is electrically connected to a correspondingtrace on one of layers 122, 132, 142. As depicted in FIG. 4B, brush 80is connected to a trace in layer 142. The brush 80 has a leg portion 170and a curved portion 172 at a distal end thereof. The curved portion 172has a rounded surface 174 in mechanical and electrical contact with anelectrical ring 84 in the electrical slip ring 41. Each brush is platedwith nickel plating and then gold plated.

Referring now to FIGS. 5A-5L, the process of manufacturing an electricalslip ring according to the present invention is illustrated. The processdescribed below is for manufacturing each of the electrical slip ringhalves 54, 56 described above having densely packed electrical rings 80.It should be noted that any number of electrical rings can be formed ona substrate according to the present invention although only three ringsare depicted in the partial elevational side views of FIGS. 5A-5L forease of discussion.

A double sided copper laminate is first formed, although as depicted inFIG. 5A, only one copper layer is depicted on which the electrical ringsare formed. The electrically interconnecting circuits are not describedfor clarity. As depicted in FIG. 5A, a substrate 200 has a copper layer210 laminated thereon. As depicted in FIG. 5B, a plurality of holes 240are drilled through the substrate 200 and the copper layer 210. Thecopper layer 210 is then coated with a photosensitive polymer andexposed to intense ultraviolet light through a photographic negative.The other side is similarly exposed to form the electricalinterconnections. The photosensitive polymer is then developed with asolvent that selectively dissolves away unexposed areas of the resistleaving rings of developed resist 220 as depicted in FIG. 5A.

As depicted in FIG. 5C, the holes 240 are plated with an electricallyconductive material utilizing plated through holes processes and/or byfilling the holes with an electrically conductive material, such assilver filled epoxy. As depicted in FIG. 5D, multiple layers ofphotoresist 252, 254, 256 are applied to the copper layer 210.Photoresist is again applied to both sides of the slip ring circuitboards. Although not depicted in FIG. 5, a single layer of resist isapplied to the electrical interconnects.

As depicted in FIG. 5E, the multiple layers of photoresist 252, 254, 256are then exposed with ultraviolet light through a phototool containingmultiple concentric rings creating slots 262, 264, 266 for rings. Asdepicted in FIG. 5F after the image is developed, copper is thenelectroformed up between the concentric rings of photoresist to form thecopper rings 272, 274, 276. As depicted in FIG. 5G, after the resistbetween the electroformed rings is removed, the electroformed theelectroformed rings are subsequently separated by etching away the thinlayer of copper between the base of the rings, thereby electricallyisolating the rings 272, 274, 276, as depicted in FIG. 5H. As depictedin FIG. 5I, the rings 272, 274, 276 are lightly sanded to flatten thetop surface of the rings. A layer of photoresist 280 is applied to thesanded top surface of the rings. As depicted in FIG. 5J, the photoresist 280 is developed to expose the top surface of the rings. Asdepicted in FIG. 5K, the grooves 86 are etched into the top surface ofeach of the rings 272, 274, 276. As depicted in FIG. 5L, the layer ofdeveloped photoresist 280 is removed and the rings 272, 274, 276 areready for nickel and gold plating.

The rings 272, 274, 276 include grooves 86 that are approximately0.00825-0.010 inches wide. The rings 272, 274, 276 have a thickness ofbetween approximately 0.012-0.014 inches. The rings 272, 274, 276 can beas close as 0.070 inches apart.

When the slip ring 41 is mated with brush block assemblies, it isimportant that the brush pressure be consistent over repeated cyclingthrough the operational temperature range of −54° C. to +60° C.

To maintain boundary lubrication at low temperatures, there must be alubricant placed on the electrical slip rings in the grooves 86 whichmust have fluid viscosity remaining low enough to prevent theviscosity/velocity product from reaching some critical value at whichpoint the hydrodynamic lift will cause the contacts to separate. Thecritical value is a function of lubricant viscosity and lubricantquantity. Even though the quantity of lubricant required for boundarylubrication is smaller than that needed for full film lubrication, to adegree, the greater the quantity of lubricant present, the longer willbe the life of the slip ring. But the greater the quantity, the easierit is for the lubricating mechanism to change from boundary lubricant tohydrodynamic lubrication, as the lubricant viscosity increases. Enoughlubricant must be present, but not too much lubricant. Adding to thedilemma, fluids at work at very low temperatures are so volatile at roomtemperature (and higher) that they vaporize in a relatively short time.To reduce friction, a lubricant is used between the contact services andare coated with a lower molecular weight linear perfluoropolyether fluidor “Z” fluid, which have much improved viscosity indices (two to threetimes that of conventional fluid lubricants) and low vapor pressures,permitting operation over wider temperature ranges. Excessive wear cancause electrical noise and other electrical problems.

It should now be apparent that an electrical slip has been describedthat achieves high bandwidth. The present invention allows a groundplane between each layer of circuits, allows adjustment of ring andground separations to minimize crosstalk and impedance mismatch, allowsuse of lubricants that remain fluid at low temperatures and provideadequate lubricity in low quantities, minimizes contamination of thematerials during the ring buildup process that might cause high noise,and prevents formation of corrosion products on ring sidewalls throughthe use of a nickel barrier coat.

It will be readily seen by one of ordinary skill in the art that thepresent invention fulfills all of the objects set forth above. Afterreading the foregoing specification, one of ordinary skill will be ableto affect various changes, substitutions of equivalents and variousother aspects of the invention as broadly disclosed herein. It istherefore intended that the protection granted hereon be limited only bythe definition contained in the appended claims and equivalents thereof.

What is claimed is:
 1. A double sided flat composite electrical slipring product produced by the method comprising the steps of: forming aplurality of concentric spaced electrical contacts on one side of afirst non-conductive base and forming interconnecting electrical pathson an opposite side of the first non-conductive base; forming aplurality of concentric spaced electrical contacts on one side of asecond non-conductive base and forming interconnecting electrical pathson an opposite side of the second non-conductive base; electricallyconnecting the electrical contacts and the interconnecting electricalpaths on said first non-conductive base; electrically connecting theelectrical contacts and the interconnecting electrical paths on thesecond non-conductive base; depositing copper on the electrical contactsto form electrical rings on the first non-conductive base; depositingcopper on the electrical contacts to form electrical rings on the secondnon-conductive base; etching a groove into each of the electrical rings;and placing the opposite sides of the first and second non-conductivebases together to form the double sided flat composite electrical slipring product.
 2. The flat composite electrical slip ring productproduced by the method of claim 1, comprising forming a double sidedcopper clad laminate on the non-conductive base, the copper cladlaminate having a first side and a second side.
 3. The flat compositeelectrical slip ring product produced by the method of claim 1,comprising coating at least one of the first side and the second sidewith a photosensitive polymer and exposing selected areas of thephotosensitive polymer to a light source.
 4. The flat compositeelectrical slip ring product produced by the method of claim 1,comprising dissolving away unexposed areas of a photosensitive polymerto expose copper cladding underneath and etching away exposed coppercladding.
 5. The flat composite electrical slip ring product produced bythe method of claims 1, comprising removing remaining unexposedphotosensitive polymer and depositing copper on the exposed coppercladding to form built-up electrical contacts.
 6. The flat compositeelectrical slip ring product produced by the method of claim 1,comprising coating built-up electrical contacts with a photosensitivepolymer.
 7. The flat composite electrical slip ring product produced bythe method of claim 1, comprising exposing selected areas of thephotosensitive polymer to a light source and dissolving away exposedareas of the photosensitive polymer to expose copper cladding underneathand etching away exposed copper cladding to form grooves in eachbuilt-up electrical contacts to form the electrical rings.
 8. The flatcomposite electrical slip ring product produced by the method of claim1, wherein the forming step includes forming a double sided copper cladlaminate on the non-conductive base, the copper clad laminate having afirst side and a second side, coating one of the first side and thesecond side with a photosensitive polymer and exposing selected areas ofthe photosensitive polymer to a light source, and dissolving awayunexposed areas of the photosensitive polymer to expose the coppercladding underneath and etching away exposed copper cladding.
 9. Theflat composite electrical slip ring product produced by the method ofclaim 1, wherein said electrical connecting step includes drilling atleast one hole through said non-conductive base and filling the at leastone hole with an electrically conductive material.
 10. The flatcomposite electrical slip ring product produced by the method of claim1, further comprising applying a photosensitive polymer and wherein saiddepositing copper step includes removing remaining unexposedphotosensitive polymer and depositing copper on the exposed coppercladding to form built-up electrical contacts.
 11. The flat compositeelectrical slip ring product produced by the method of claim 1, whereinsaid etching step includes coating built-up electrical contacts with aphotosensitive polymer and exposing selected areas of the photosensitivepolymer to a light source and dissolving away exposed areas of thephotosensitive polymer to expose copper cladding underneath and etchingaway exposed copper cladding to form grooves in each of the built-upelectrical contacts to form the electrical rings.
 12. The flat compositeelectrical slip ring product produced by the method of claim 1, whereinthe grooves are approximately between 0.008 to 0.010 inches.
 13. Theflat composite electrical slip ring product produced by the method ofclaim 1, wherein said depositing step is performed before electricallyconnecting step.
 14. The flat composite electrical slip ring productproduced by the method of claim 1, wherein said electrically connectingstep is performed before said depositing step.
 15. A double sided flatcomposite electrical slip ring, comprising: a first electricallynon-conductive base having a first side and a second side; a firstplurality of concentric spaced electrical rings located on said firstside of said first electrically non-conductive base, said slip ringsbeing spaced from adjacent electrical rings at a distance ofapproximately 0.070 inches or greater; a second electricallynon-conductive base having a first side and a second side; a secondplurality of electrical rings located on said first side of said firstelectrically non-conductive base, said slip rings being spaced fromadjacent electrical rings at a distance of approximately 0.070 inches orgreater; first interconnecting electrical paths located on said secondside of said first electrically non-conductive base; secondinterconnecting paths located on said second side of said secondelectrically non-conductive base; first connecting means for connectingsaid first plurality of electrical rings to said first interconnectingpaths; second connecting means for connecting said second plurality ofelectrical rings to said second interconnecting paths wherein saidsecond side of said first electrically non-conductive base and saidsecond side of said second electrically non-conductive base are abuttingeach other.
 16. The slip ring of claim 15, wherein each of said firstand second electrically non-conductive bases are rotatable with acentral shaft.
 17. The slip ring of claim 16, further comprising aU-shaped annular frame stacker, each of said electrically non-conductivebases having an outer edge supported by said U-shaped frame stacker. 18.The slip ring of claim 15, further comprising a first brush blockassembly in electrical contact with said first plurality of electricalrings and a second brush block assembly in electrical contact with saidsecond plurality of electrical rings.
 19. The slip ring of claim 15,wherein each of the electrical rings has a thickness of approximatelybetween 0.012 to 0.014 inches.
 20. The slip ring of claim 15, furthercomprising a plating on each of the plurality of electrical rings. 21.The slip ring of claim 15, wherein each of the electrical rings hasgrooves which are approximately between 0.008 to 0.010 inches wide.